General solution: \begin{equation} u = \phi(x+ct) + \psi(x-ct) \end{equation} for general form \begin{equation} u_{tt} - c^{2}u_{xx} = 0 \end{equation}

All of the equations in this question satisfy this general form with c=1, 2, 3, 1/2, 3 (possible mistake of the question, should put 9 in front of the first term, if so c = 1/3).

plug the corresponding c into the general solution we have the answer for each equation.